Tidal Depth Research Articles

An outlier-robust Rao–Blackwellized particle filter for underwater terrain-aided navigation

Terrain-aided navigation (TAN) is one of the key techniques for autonomous navigation and positioning of AUVs. This paper develops a novel integrated navigation system that combines the inertial navigation system (INS) and TAN into one filter, in contrast to the conventional INS/TAN model. This method not only provides a position estimate for the carrier but also the INS error, which increases the filtering dimension significantly. Thus, the Rao-Blackwellized particle filter (RBPF) technique is introduced to address the “dimensional disaster” problem. A three-dimensional (3-D) model is established to estimate the horizontal position while compensating for the tidal inaccuracy by extending the tidal depth bias to the state space. Furthermore, the variable and complex underwater environment can potentially result in outlier interference in depth measurements, which significantly degrades the performance of the RBPF-based estimation algorithm. This paper thus presents a 3-D adaptive RBPF method based on the maximum correntropy criterion (MCC) to suppress the influence of measurement outliers on positioning precision. Simulations and experimental tests verify the effectiveness of the proposed algorithm. The results demonstrated that the 3-D model-based AMCCRBPF method can effectively improve robustness to outliers and provide an accurate estimate of the tidal depth bias.

Flowering variabilities in subtropical intertidal Zostera muelleri meadows of Australia

Flowering is an integral feature of the life history of seagrasses, and it contributes to the genetic diversity and resilience of meadows. There is some evidence that seagrass flowering is influenced by tidal depth; however, the effects of tidal exposure on the flowering variabilities in patchy intertidal meadows are largely unknown. In the present study, inter and intra-annual variability of flowering was examined using a line transect sampling method across two subtropical intertidal meadows (i.e., Lilley’s Beach and Pelican Banks) of Zostera muelleri on Australia’s east coast. Along each transect, the depth was measured using Leica Geosystems AGS14 RTK, and the plant cover was estimated using a standard scale. The duration of exposure at each depth was computed based on the tidal data and categorised exposure duration by hours. The abundance (i.e., the density of flowering shoots and density of spathes) and the ratio of flowering (i.e., flowering frequency) and morphology of flowering (i.e., the number of spathes per flowering shoot) were estimated at every 10 m along three 100 m fixed transects established perpendicular to the tide monthly in 2020 and 2021. Flowering started in July and extended for approximately six months, with peak flowering observed in September-October at both sites. Generalised linear mixed-effect models showed that approximately 39% of the density of flowering shoots, 36% of the density of spathes and 28% of flowering frequency were explained by plant cover and exposure duration. Similar variation in the spathes per flowering shoot was explained by plant cover only (40%). The density of spathes during peak flowering months was significantly different among exposure categories (3-4 hrs and 5-6 hrs in Lilley’s Beach and 5-6 hrs and 6-7 hrs in Pelican Banks in 2021), where significantly different interannual variability was observed only between the same exposure categories in Pelican Banks. The study offers valuable insights into seed-based restoration projects, including optimal seed harvesting times and the average quantity of harvestable flowers, although some inter-annual variations should be anticipated.

Simulated megaherbivore grazing as a driver of seagrass flowering

Seagrass meadows are an important habitat for Testudines (sea turtles) and Sirenia (dugong and manatee) megaherbivores. Megaherbivores can influence the structuring of seagrass meadows; for example, foraging patterns have been found to relate to seagrass phenological strategy. However, as these observations are derived from uncontrolled field studies, it is unclear whether grazing drives such changes or if the changes are related to other factors (e.g., temperature, tidal depth, light). In the present study, a mesocosm experiment was designed to test the impacts of grazing on metrics of flowering of Zostera muelleri over two consecutive flowering seasons. Prior to each flowering season, plants were cropped to 3 cm and 1 cm lengths to represent turtle and dugong grazing, respectively. This study measured the timing of flowering, the number of flowering shoots, the height of the flowering shoot, and the number of spathes (sheathing bracts containing seeds) per flowering shoot in each replicate (n = 5) weekly. Cropping had no significant influence on the timing of flowering (i.e., number of days to first and peak flowering) indicating that it is not a trigger for flowering. However, cropping significantly reduced the maximum density of flowering shoots and spathes, which was proposed to be due to resource allocation differences between clonal growth and flower production. A reduction in the flowering ratio was observed in both cropped plant groups and the relatively high density and the ratio of flowering observed in the 1 cm group indicate that the plant was adapting to cope with stress. Morphology of flowering (i.e., the maximum height of flowering shoot and the maximum number of spathes per flowering shoot) was not significantly affected by cropping and these two variables were strongly correlated. The results suggest that cropping can influence the overall flowering densities in a season but not the timing of flowering. This study demonstrated that cropping prior to the flowering season can reduce the expected production of spathes in seed nurseries and suggests it may be beneficial to consider megaherbivores in seed-based restoration activities.

Land assessment for Sonneratia caseolaris (L.) Engl. development in mangrove forest areas of coastal Nghe An Province

Assessment of potential mangrove land suitability for mangrove tree species is a multi-objective analysis and decision-making problem in coastal mangrove development planning. In this study, GIS technology is applied to assess ecological adaptation for Sonneratia caseolaris (L.) Engl. There are 16 indicators of 4 criteria used: (i) Type of mangrove land, (ii) Substrate and soil texture, (ii) Tidal depth, and (iv) Status of mangroves and mangroves. There are 127 land units evaluated for Sonneratia caseolaris (L.) Engl., of which 77 land units are highly adaptive (198.5 ha, accounting for 19.5%), 20 of land units are at the medium adaptability (139.7 ha, 27.7%), 0 land units are less adapted and the rest are unadapted (377.6 ha, 52.7%). The result is a scientific basis for the planning of mangrove forest development in the coastal area of Nghe An Province.

Tidal stream use by black guillemots Cepphus grylle in relation to a marine renewable energy development

Seabirds that forage within tidal streams may be vulnerable to collision or habitat change due to tidal stream turbines. The black guillemot Cepphus grylle is considered to be the seabird species most at risk from tidal stream turbines in UK waters. Using GPS tracking of adult breeding black guillemots, carried out on the island of Stroma, Caithness, in 2016 and 2017, we examined habitat use within the Inner Sound of the Pentland Firth in relation to the MeyGen tidal lease area (MTLA). We found foraging areas of black guillemots within the Inner Sound to be influenced by tidal velocity and seafloor depth. The velocities and depths which black guillemots selected while foraging within a 1 km boundary of the lease area significantly differed from those concurrently occurring within the MTLA (velocities: foraging = 0.79 m s-1, MTLA = 1.57 m s-1; depths: foraging = 24.55 m, MTLA = 32.09 m). This disparity between the used habitat and the conditions within the MTLA may indicate a reduced potential for interactions with turbines. The potential for collision with turbine blades is further reduced by black guillemots predominantly associating with mean tidal velocities slower than the 1 m s-1 cut-in speeds of the MeyGen turbines. However, as more turbines are constructed within the lease area (up to 398 turbines proposed), habitat and hydrodynamic conditions may be altered to become more suitable for foraging, so monitoring black guillemot foraging behaviour post-construction is strongly recommended.

Elasmobranch (Chondrichthyes, Elasmobranchii) Habitat Use in an Insular Tropical Lagoon in Exuma, The Bahamas

Elasmobranchs (sharks, rays, skates, and sawfish) exert top-down pressure in tropical lagoons and are necessary for maintaining trophic balance, so it is important to understand how abiotic factors drive shark and ray movement and habitat use in a tropical lagoon. Our aim was to assess patterns of lagoon use by sharks and rays in Anne's Creek, Exuma, The Bahamas. Four different elasmobranch species (Hypanus americanus, Styracura schmardae, Ginglymostoma cirratum, and Negaprion brevirostris) were observed using non-invasive visual surveys from the mouth of the lagoon in the summer of 2019 and the winter of 2020. Ray presence was significantly higher in the winter than in the summer and their presence is negatively correlated with temperature in the winter, which suggests a preference for cooler temperatures that affects ray nearshore habitat use. Ray presence was also changed with tidal phase and was weakly negatively correlated with tidal depth. Shark presence was not significantly correlated with season, temperature, or tides – this could be due to low sample sizes as sharks were less abundant than rays. Ultimately, understanding abiotic forces that drive shark and ray habitat use can help predict how they may respond to temperature changes and sea level rise associated with climate change.

Coastal Wetland Mapping Using Ensemble Learning Algorithms: A Comparative Study of Bagging, Boosting and Stacking Techniques

Coastal wetlands are a critical component of the coastal landscape that are increasingly threatened by sea level rise and other human disturbance. Periodically mapping wetland distribution is crucial to coastal ecosystem management. Ensemble algorithms (EL), such as random forest (RF) and gradient boosting machine (GBM) algorithms, are now commonly applied in the field of remote sensing. However, the performance and potential of other EL methods, such as extreme gradient boosting (XGBoost) and bagged trees, are rarely compared and tested for coastal wetland mapping. In this study, we applied the three most widely used EL techniques (i.e., bagging, boosting and stacking) to map wetland distribution in a highly modified coastal catchment, the Manning River Estuary, Australia. Our results demonstrated the advantages of using ensemble classifiers to accurately map wetland types in a coastal landscape. Enhanced bagging decision trees, i.e., classifiers with additional methods to increasing ensemble diversity such as RF and weighted subspace random forest, had comparably high predictive power. For the stacking method evaluated in this study, our results are inconclusive, and further comprehensive quantitative study is encouraged. Our findings also suggested that the ensemble methods were less effective at discriminating minority classes in comparison with more common classes. Finally, the variable importance results indicated that hydro-geomorphic factors, such as tidal depth and distance to water edge, were among the most influential variables across the top classifiers. However, vegetation indices derived from longer time series of remote sensing data that arrest the full features of land phenology are likely to improve wetland type separation in coastal areas.

Review of Tide and Wind Affect to Currents Pattern in Amurang Bay, North Sulawesi, Indonesia

Winds, tides and river discharges largely drive coastal currents. The strength of tidal currents, river runoff, meteorological conditions, shoreline configuration, water depth and topography are the factors that affect coastal water circulation. Generally currents are the flowing of water mass caused by wind, difference of density or tide moving. The existence of currents direction to nearshore of Amurang Bay was studied with using computer model tools as the hydrodynamic model by determine currents speed and its direction.The study took place in Amurang Bay as the province of North Sulawesi Indonesia with the geography position around 1012’16.16” N-124027’04.33” E to 1015’43.80” N-124032’01.06”E. The bathymetry and tide data used in this research from Indonesian Coastline Environmental map of year 1995 with scale 1:50.000 from BIG (Badan Informasi Geospasial) with a satellite data from Google earth of year 2018 and LANTAMAL Manado, the wind and current data was obtained from BMKG Bitung. Time simulations are taken from 25 November to 23 December 2016 as a wet season and 25 Mei to 23 Juni 2016 as a dry season. As analytical tools, MIKE3 hydrodynamic mode are used. The currents pattern play an important role in sediment transport process, so the study of the currents pattern become to be important as well. The result of this study indicate that in the wet season the combination of tide wind in surface and bottom layer of sea the currents direction close to nearshore dominant to East with current speed average 0.18 m/s, in dry season the combination of tide wind in surface layer of sea the currents direction close to nearshore dominant to South-East with current speed 0.12-0.24 m/s, in bottom layer the currents direction dominant to South-East with current speed average 0.2 m/s. Some of interesting point in research’s area show that current by tide make the current direction seaward and landward, but tide combination wind change the direction of current. It can be said that the tide influenced to current make the currents direction seaward and landward follow the pattern of tide, but combination tide and wind change its direction.

Marginalized Point Mass Filter with Estimating Tidal Depth Bias for Underwater Terrain-Aided Navigation

Terrain-aided navigation is a promising approach to submerged position updates for autonomous underwater vehicles by matching terrain measurements against an underwater reference map. With an accurate prediction of tidal depth bias, a two-dimensional point mass filter, only estimating the horizontal position, has been proven to be effective for terrain-aided navigation. However, the tidal depth bias is unpredictable or predicts in many cases, which will result in the rapid performance degradation if a two-dimensional point mass filter is still used. To address this, a marginalized point mass filter in three dimensions is presented to concurrently estimate and compensate the tidal depth bias in this paper. In the method, the tidal depth bias is extended as a state variable and estimated using the Kalman filter, whereas the horizontal position state is still estimated by the original two-dimensional point mass filter. With the multibeam sonar, simulation experiments in a real underwater digital map demonstrate that the proposed method is able to accurately estimate the tidal depth bias and to obtain the robust navigation solution in suitable terrain.

Planning Navigation in Inland Waterways with Tidal Depth Restrictions

The planning of vessel navigation along a tidal river is a complex task that can affect the efficiency of inland ports and intermodal chains. The availability of water may represent a significant restriction to port accessibility, having an impact on waiting times, cost and even safety. This paper presents a heuristic procedure to schedule vessels on a tidal waterway, which seeks to optimise navigation according to a multi-criteria objective function combining the number of vessels serviced, the total waiting time, the waterway occupation time and the number of crossing operations, where the term “crossing” implies inbound and outbound vessels passing each other. The procedure requires a previous step of estimation of real-time water depth, which identifies the critical points or navigation bottlenecks along the waterway, and contemplates the possibility of vessels having to anchor in the middle of their journey and wait for next tide rise. We validate the procedure through its application to a set of real and test problems and show that its results are reliable in terms of performance and solution quality.

Salinity and suspended sediment transport in a shallow estuary on the east coast of India

Velocity, salinity, tidal depth and suspended sediment concentrations were monitored at the two stations located at the mouth and head of the Muthupet estuary during the spring and neap tides of post-monsoon, pre-monsoon and monsoon seasons. There was a pronounced seasonal variation in the salinity and suspended sediment concentration during the study period. The total transport of salt at the station near the mouth varied between 4.78 kg/s/m and 0.038 kg/s/m. The transport of suspended sediments was in the range of 0.021 kg/s/m and 0.121 kg/s/m. The direction of transport of salt and suspended sediments also varied over a seasonal scale. The transport of salt and suspended sediments occurred in the downstream direction during the post-monsoon and monsoon, while it was in the upstream direction during the pre-monsoon. Fluvial advection was identified as the main controlling factor in the transport of salt and suspended sediments. The formation of salt plug during the pre-monsoon affected the transport of salt; the transport of salt was from the location of salt plug to the upstream and downstream directions. The spatial variability in the transport of suspended sediments was evident, with higher transport at the downstream station than that at the upstream station. The transport of salt was correlated with the concentration of Fe in the estuary obtained from previous studies. Further, it was observed that the concentration of Cd and Cu was dependent on the resuspension of sediments due to tidal action. The study proved that all the suspended sediments transported towards the upstream from the downstream reaches do not reach the upstream station, but are removed from the water column; the transport of suspended sediments were correlated with the settling velocity established from previous studies.

EFECTOS DE LAS MAREAS Y DE LOS PERÍODOS INTRA ESTACIONALES EN EL COMPORTAMIENTO DE LOS CORMORANES PELÁGICOS (Phalacrocorax pelagicus Pallas, 1811) DURANTE EL BUCEO EN CATTLE POINT, SAN JUAN ISLAND, WASHINGTON, U.S.A

The influence of time of day, tidal depth, current and inside-season change on the diving behavior of pelagic cormorants, as well as the relationships between diving time and the preceding and the subsequent surface time were examined at Cattle Point, San Juan Island. Diving behavior was recorded using focal animal sampling. Dives and surfaces were timed to the nearest second. Correlations between dive time and the other variables were analyzed using regression analysis and t-test of significance. On a daily basis, dive times varied with time of day, tidal depth and current direction. Dive times were longer later in the day, showing a trend to be longer when height of the tide was higher and during ebb tides. However, dive times remained variable throughout the course of the season. No inside-season related variation on diving times was found, probably due to changes in prey availability. Mean dives and recovery times were 31.2 sec and 19.1 sec respectively showing that dive times were longer than surface times. Even so, positive relationships were found between dive time and the preceding surface time and between dive time and the subsequent surface time suggesting that cormorants utilize both anticipatory and reactive breathing according to the foraging environment.

Observations and model simulations of wave‐current interaction on the inner shelf

AbstractWave directions and mean currents observed for two 1 month long periods in 7 and 2 m water depths along 11 km of the southern shoreline of Martha's Vineyard, MA, have strong tidal modulations. Wave directions are modulated by as much as 70° over a tidal cycle. The magnitude of the tidal modulations in the wavefield decreases alongshore to the west, consistent with the observed decrease in tidal currents from 2.1 to 0.2 m/s along the shoreline. A numerical model (SWAN and Deflt3D‐FLOW) simulating waves and currents reproduces the observations accurately. Model simulations with and without wave‐current interaction and tidal depth changes demonstrate that the observed tidal modulations of the wavefield primarily are caused by wave‐current interaction and not by tidal changes to water depths over the nearby complex shoals.

Mangrove (Avicennia marina subsp. australasica) litter production and decomposition in a temperate estuary

Mangrove forests can provide important cross-boundary subsidies of organic matter to adjacent habitats through the production, export, decomposition and assimilation of litter. We quantified two of these components in a temperate mangrove forest in Whangamata Harbour, New Zealand: 1) litter production; and 2) decomposition rates as a function of tidal elevation, sediment type and burial depth. Litter traps sampled monthly for a year measured an annual detrital input of 3.24–5.38 t DW ha−1, of which 77% occurred in summer. Decomposition rates depended on litter type, with leaves decomposing faster (63 d to decay by 50%) than pneumatophore and wood material (316 and 460 d, respectively). Buried leaf and wood litter decomposed 1.3–1.4 times slower than litter on the sediment surface; however, tidal elevation and sediment type (mud vs. sand) had no effect. The slow decay of litter (an order of magnitude slower than tropical mangrove litter) suggests that its incorporation into temperate marine food webs may be relatively slow.

Numerical modeling of low-frequency wave dynamics over a fringing coral reef

Low-frequency (infragravity) wave dynamics on a fringing coral reef were investigated using the numerical model XBeach (Roelvink et al., 2009). First, the skill of the model was evaluated in one- and two-dimensions based on its predictions of short waves (0.04–0.2Hz), infragravity waves (0.004–0.04Hz) and water level measurements (tidal and wave setup) obtained during a 2009 field study at Ningaloo Reef in Western Australia. The model calibration was sensitive to friction coefficients for short waves and current/infragravity bed friction, which were assumed independent in this model study. Although the one-dimensional cross-shore model captured the gradients in the dominant hydrodynamic processes at the site, a high current/IG bed friction coefficient was required. This resulted in an overestimation and a phase lag between the observed and predicted wave setup signal. In the two-dimensional model, a lower (more realistic) current/infragravity wave friction coefficient was required to achieve optimum performance due to the presence of significant reef and lagoon mean flows in the model, which led to reduced setup across the reef. The infragravity waves were found to propagate from the surf zone across the reef in a dominantly cross-shore direction towards the shore, but with substantial frictional damping. The infragravity waves were strongly modulated also over the reef by tidal depth variations, primarily due to the variability in frictional dissipation rates when the total water depth over the reef varied. Two mean wave-driven circulation cells were observed in the study area, with cross-shore flow becoming more alongshore-dominated before exiting the system via the two channels in the reef. The results reveal that short waves dominated bottom stresses on the forereef and near the reef crest; however, inside the lagoon, infragravity waves become increasingly dominant, accounting up to 50% of the combined bottom stresses.

MODELLING INFRAGRAVITY WAVES AND CURRENTS ACROSS A FRINGING CORAL REEF

Low-frequency (infragravity) wave dynamics on a fringing coral reef were investigated using the numerical model XBeach (Roelvink et al, 2009). First, the skill of the one-dimensional model was evaluated based on its predictions of short waves (0.04-0.2 Hz), infragravity waves (0.004-0.04 Hz) and water level measurements (tidal and wave setup) obtained during a 2009 field study at Ningaloo Reef in Western Australia. The model calibration was sensitive to friction coefficients for short waves and current / infragravity bed friction, which were assumed independent in this model study. The infragravity waves were found to be generated primarily in the surf zone through the breakpoint generation mechanism rather than through offshore forcing. The infragravity waves were strongly also modulated over the reef by tidal depth variations, primarily due to the variability in frictional dissipation rates when the total water depth over the reef varied. The results reveal that short waves dominated bottom stresses on the fore reef and near the reef crest; however, inside the lagoon, infragravity waves become increasingly dominant, accounting up to 50% of the combined bottom stresses

Investigating enhanced atmospheric–sea surface coupling and interactions in the Irish Sea

Enhanced atmospheric–sea surface coupling is investigated in the Irish Sea. The implications for so-called Proudman resonance are considered for a hindcast of an event that produced a significant, pressure-induced storm surge at the port of Liverpool. Time-series of non-dimensional gain along the depression track show resonant enhancement of the pressure-driven residual elevations in the central, deeper region of the Irish Sea when a depression moves at the speed of a shallow water wave (gh 0.5 ). However, in the relatively shallow eastern Irish Sea the wind stress is the dominant surge-generating mechanism. Wind-generated surge magnitude is influenced by the propagation speed of the depression which controls the timing of momentum input with respect to tidal depth variations. Large surges at Liverpool are mostly caused by an almost linear summation of the wind- and pressure-induced surge components when the wind stress acts over low water and/or the rising tide. However, it is possible for the interaction of wind stress and pressure to reduce the total surge when a pressure-induced sea-level increase reduces the effect of the wind stress. The Irish Sea is too small for significant resonant enhancement due to atmospheric–sea surface coupling and surge magnitudes are strongly dependent on the intensity of the depression and the magnitude of the wind stress. ► Proudman resonance can occur in a limited region of the Irish Sea. ► Resonant sea-level increase is less significant than other factors. ► Non-linear interaction between wind- and pressure-driven surges. ► Surges dependent on the strength of the wind stress and depression intensity.

Seasonal Behaviour of a Shallow Estuary of Lower Cauvery Basin, India

The effect of bifurcation at the estuary mouth was studied on the measurements of salinity, current and tidal depth in a shallow estuary during spring and neap tides of two different seasons. There was a considerable variation of salinity at the observed stations during the seasons. At the shallowest location of the estuary, salinity, as high as 37 ppt, was observed during the period of zero fresh water discharge. The flushing time of the estuary was higher at its western side compared to the eastern one. The diffusion coefficient was reached by using an advection-diffusion equation. The estuary was classified using a circulation/stratification diagram. Well mixed conditions persisted during pre monsoon and post monsoon in the Muthupet estuary. DOI: http://dx.doi.org/10.5755/j01.erem.61.3.2041

Vertical Distribution of Turbulence Shear Stress During Tidal Period

Turbulence shear stress is an important dynamic characteristic of flow in tidal channel. In the paper, the new vertical distribution of the tidal turbulence shear stress, which can reflect the development of the stress profile over the tidal period, is proposed. The comparison between computed result and the data from field and experiment measurements indicates that the proposed vertical distribution which agrees well with the measurements can well depict the upward concave distribution in phase of accelerating process and upward convex in phase of decelerating process. Through analyzing the amplitude and phase variation along the depth on different conditions, it is found that it is the nondimensional parameter , namely the ratio of tidal period, turbulence intensity and water depth that determines the form of turbulence shear stress distribution during tidal period.

Prey capture success and chick diet of Damara terns Sterna balaenarum in Namibia

Feeding terns are affected by a variety of environmental conditions. We studied prey capture success of Damara terns Sterna balaenarum in relation to six variables at two breeding colonies in southern Namibia: tidal phase, wind speed, water clarity, cloud cover, water depth and locality. Damara terns dived most successfully at high tide and least successfully at low tide. Prey capture success improved whereas total dive rate decreased with increasing wind speed. Prey capture success was highest in the least turbid water, but was not significantly affected by cloud cover or water depth, and there was no significant difference in dive success between localities. The diet of Damara tern chicks were studied throughout Namibia. Of 55 prey items collected, Cape silverside Atherina breviceps, southern mullet Liza richardsonii and Cape anchovy Engraulis encrasicolus were among the most abundant prey species. At least nine prey species were found in the diet of Damara tern chicks that had not been previously reported from Namibian waters